Semiconductor device manufacturing methods often employ back end of line (BEOL) processes to add interconnect wiring to integrated circuit (IC) devices. For example, in numerous applications, multiple layers of dielectric material (often referred to as interlayer dielectric, or ILD) are formed on a chip. The layers of dielectric material are patterned and etched to form trenches that are later filled with conducting material (e.g., copper) to form vias and wires that connect devices (e.g., RAM) in the chip to other components (e.g., motherboard). Conventional high speed chips may have as many as five to ten wiring layers.
Historically, dense metal oxides such as, for example, silicon dioxide (SiO2), have been used as the dielectric material in interconnect structures. While SiO2 is an excellent insulator with high modulus and hardness, and has a coefficient of thermal expansion (CTE) close to silicon, the dielectric constant (k) is approximately 4.0, which is too high for advanced generation interconnects. As such, device manufacturers are migrating toward the use of low-k (e.g., k<3.0) dielectric materials (such as, for example, inorganic polymers, organic polymers such as polyamides, spin-on glasses, silsesquioxane-based materials, etc.). Generally speaking, low-k dielectric materials serve to increase the speed of the conducting wires, thereby increasing the speed of the semiconductor device.
However, integrating low-k dielectric materials into the wafer BEOL results in delamination stresses that occur when the chip is packaged. The delamination of the chip in the low-k dielectric material layers due to their weaker mechanical properties (e.g., modulus and adhesion) may result in failure of the semiconductor device.
For example, stresses are imparted to the chip due to differences in CTE between the chip and the different materials used in semiconductor packaging. Illustratively, a Silicon chip has a relatively low CTE, while an organic carrier that the low-k chip is disposed upon may have a relatively high CTE. Also, each wiring level may be composed of a different low-k dielectric material, each having differing coefficients of thermal expansion. When the chip is assembled to an organic carrier at an elevated temperature and subsequently cooled, and when a chip undergoes thermal cycling during reliability testing, the differences in CTE between adjacent layers cause stresses at the interface between the layers. These stresses can lead to structural damage of the chip, including cracks in individual layers and delamination between adjacent layers, also known as “white bumps”. Structural damage, in turn, renders a chip unusable, thereby decreasing yield and posing a reliability risk.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.